Mobile devices can provide both voice-based connections and packet-based data connections using different base stations and infrastructures. For example, a Web-enabled cell phone might maintain a voice connection using a first transmission channel and maintain a mobile IP connection using a second (and independent) transmission channel, such that handoffs occur independently for the two channels. Alternatively, voice services can be combined with packet services, such that a single connection is maintained for both services. Voice connections can also be provided over IP in a combined service.
FIG. 1 shows a network with mobility features that covers three service areas SA1, SA2, and SA3. As shown in FIG. 1, a mobile terminal MT is within service area SA1 served by base station BS1 (also called an access point or AP). A service area generally refers to the radio coverage associated with a radio tower/base station.
Base station BS1 is connected to an access router AR1, which provides access to the Internet. Other base stations such as BS3 may also be connected to access router AR1, such that a common IP address is used for mobile terminals even though the terminals may pass through different service areas. In other words, although there may be a hand off of radio frequency channels when the mobile terminal moves between service area SA1 and service area SA3, it may not be necessary to change the IP address used to communicate with the mobile terminal because the Internet connection is still served by the same access router AR1.
A second service area SA2 is served by a separate base station BS2, which is in turn connected to a different access router AR2. Due to the network topology, access routers AR1 and AR2 use different blocks of IP addresses for communicating with mobile terminals roaming within their associated service areas. If mobile terminal MT moves from service area SA1 to service area SA2, some mechanism is needed to hand off the Internet connection from access router AR1 to access router AR2. Similarly, if service areas SA1 and SA2 are separated by a large logical distance (e.g., AR1 and AR2 are connected to different ISPs), some coordination mechanism is needed to permit data transmitted to a terminal previously operating in service area SA1 to be forwarded to service area SA2 if that terminal moves into area SA2.
One conventional scheme for handing off IP connections is depicted in FIG. 2. Service area SA1 is served by access router AR1, which is designated the “home agent” for communicating with a particular mobile terminal MT. While mobile terminal MT moves within service area SA1, correspondence nodes communicate with the mobile terminal using an IP address that is assigned by the access router AR1 to the mobile node. IP packets (e.g., e-mail, Web pages, and the like) are transmitted over the Internet to the home network and are forwarded to the mobile terminal through the home agent.
If the mobile terminal MT moves to a different service area SA2, served by a different access router AR2, packets that were previously transmitted to AR1 will no longer reach the mobile terminal.
One conventional approach for handing off mobile nodes is to advertise (e.g., broadcast) the existence of access router AR2 in service area SA2, such that when mobile terminal MT moves into service area SA2, it is notified of the existence of access router AR2, and it receives a new IP address for communicating within service area SA2. The mobile terminal MT then sends a binding update to home agent AR1 (e.g., through a land line LL or over the Internet), so that home agent AR1 knows the IP address that will allow packets to reach the mobile terminal in service area SA2. The home agent treats this address as a “care of” address, and all further packets to the mobile terminal's home address are forwarded to the new IP address. In essence, two separate IP addresses are used to communicate with the mobile terminal: a home agent address and a care of address that changes when the MT moves into a new service area.
When a mobile node moves from one access router to another, the packet forwarding path of sessions to and from the mobile node changes. In order to minimize the impact of a change in access routers, relevant context is transferred from the originating access router to the new access router. As described in H. Syed et al., “General Requirements for a Context Transfer Framework,” draft Internet Engineering Task Force Seamoby requirements work in progress (May 2001), the context transfer protocol entities may, in the process of establishing and supporting context transfer, acquire information that would be useful to the handover process in determining the new forwarding path; for example, the outcome of an admission control decision at a receiving access router.
A mobile terminal may move into an area that is served by two or more access routers. As with cellular telephone roaming, however, the mobile terminal may not be authorized to be handed off to certain access routers. Conventional handovers of mobile terminals from an originating access router to a target access router occur before determining whether the target access router is in fact authorized to service the mobile terminal. After the target access router accepts a handoff of a mobile terminal, it may perform a check to determine whether the mobile terminal is authorized to be serviced. If it is not, the service connection is dropped.
In other words, the handover decision from one AR to another AR is conventionally handled independently of whether the mobile terminal is authorized to roam into the network of the new AR. Typically, the mobile terminal is handed over to the new AR, then an authorization process ensues to determine whether the mobile terminal is authorized to roam into the new network. However, dropping the service connection with an unauthorized mobile terminal unnecessarily wastes resources, such as maintaining a connection with the mobile terminal for a period of time before the unauthorized service is discovered. It also wastes radio frequency spectrum, since radio resources are allocated to the mobile node prior to authorization. If the mobile node is determined not to be authorized, then radio resources must be revoked upon such determination of lack of authorization.
If there are several candidate access routers to which handover could result, for example those providing different access technologies (e.g., IEEE 802.11 WLANS or Bluetooth), a mobile node may not be authorized to roam into the network of certain service providers. Consequently, the conventional scheme for performing handoffs to access routers wastes resources and can delay handover processing.
What is needed is a system and method for addressing some or all of the aforementioned problems.